1. Neuronal Signals

2. Main Point #1
Neurons sense stimuli, interpret that stimuli, and react

3. 3 Functions Sensory input Receiving signals Integration
Interpretation and thinking
Motor output
Reactions

4. Main Point #2
The nervous system consists of neurons and supporting cells, which greatly outnumber the number of neurons

5. Cells of the Nervous System
Neurons
Carry signal throughout the body
Supporting cells (glia)
Provide structure
Protect/insulat e neurons

6. Neuron Structure Large cell body Dendrites – receive signals
Axons – carry signals to other neurons

7. Dendrites and Axons

8. Speeds up transmission of signals
Myelin Sheath
Insulation layer
Speeds up transmission of signals

9. Synapse The end of an axon is called the synaptic terminal
Connects to a target cell

10. Nerve vs. Neuron
A nerve is a bundle of neurons with similar functions
Neurons only convey signals in one direction, but a nerve can be multidirectional as it has many neurons

11. Main Point #3
Neural signals are transmitted as electrical signals in the form of action potentials, rapid changes in the voltage of a neuron

12. Neural Signals Based on ions moving in and out of neurons
Changes the voltage across the membrane

13. Sodium Potassium Pump
Pumps 3 Na+ molecules out for every 2 K+ molecules that get in
Makes inside more negative relative to outside

14. Na+ / K+
Na+ is much more concentrated outside cell, wants to diffuse in
K+ is much more concentrated in the cell, wants to move out

15. The Resting Voltage
The inside is negatively charged – relative to the outside which is by definition 0
Resting voltage is about -70mV (5% of the voltage of a flashlight)

16. Voltage gated Ion channels
Open or close depending on voltage
Let ions in or out

17. Hyperpolarization/Depolarization
Opening of the K+ channel lets K+ flow out, making cell more negative
Opening Na+ channel lets Na+ flow in, making cell become positive

18. Action Potential
When a cell reaches a depolarization threshold, voltage- gated Na channels open
Causes the neuron to quickly become very positive

19. How an Action Potential Works
2. Na+ channels close, K+ channels open, cell returns to negative
1. Na+ channels open, cell becomes positive
1. Na+ channels open, cell becomes positive
3. K+ channels stay open, cell becomes even more negative
REFRACTORY PERIOD
4. Cell returns to normal state

20. The Refractory Period Cell becomes hyperpolarized
Won't react to another stimulus
Limits how fast neurons can fire
Strong stimuli cause nerves to fire immediately after this period

21. Main Point #5
Action potentials travel down a neuron and are sped up by myelination of the axon

22. Travel of Action Potential
Na+ flowing into one part of the axon makes the portions next to it positive
This causes a new action potential
Keeps getting passed down the neuron

23. Speeding up Transmission
Bigger axons convey messages quicker
Myelinated axons have evolved in vertebrates

24. How Myelination Works Ions can only diffuse at gaps in the myelin
So the action potential jumps from node to node
Signals can move 150m/s!

25. White Matter vs. Gray Matter
Myelinated axons appear white and are bundled together
Cell bodies, dendrites and un-myelinated axons appear gray

26. Main Point #6
Signals are transmitted from a neuron to another cell at synapses
Can be stimulatory or inhibitory

27. Synapses Small gap between neuron and another cell
Can be another neuron, a muscle cell or a gland

28. Role of Calcium
At the end of the axon terminal depolarization causes opening of Ca++ channels
Inflow of calcium causes neurotransmitters stores in vesicles to be released

29. Chemical Synapses
Axon terminal releases a neurotransmitter into the synaptic cleft
The neurotransmitter binds to a receptor on the receiving cell, opening ion channels

30. Postsynaptic Effects
Some channels cause depolarization or the creation of an action potential
Some cause hyperpolarization, inhibiting action potentials

31. Summation
Usually one neuron doesn't cause a strong enough effect to cause an action potential
But a neuron receives signals from several neurons

32. Response Eventually the signal induces a response
I.e. flexing of a muscle, opening/closing of a channel, release of a hormone etc.

33. =sodium (Na+) V
-50
-70
=potassium (K+)
Time

34. Ca Ca Ca